The present invention relates to optical fiber manufacturing systems and, more particularly, to a method and apparatus for detecting various conditions in an ultraviolet (UV) curing lamp system to determine whether or not the conditions are suitable for properly curing a UV-curable material disposed in the UV curing lamp system.
The successful implementation of a light wave communication system requires high quality light guide fibers having mechanical properties sufficient to withstand the stresses to which they are subjected. Each fiber must be capable of withstanding over its entire length a maximum stress level to which the fiber will be exposed during installation and service. The importance of fiber strength becomes apparent when one considers that a single fiber failure will result in the loss of several hundreds of active telephone and data circuits.
The failure of light guide fibers in tension is commonly associated with surface flaws which cause stress concentrations and lower the tensile strength below that of pristine unflawed glass. The size of the flaw determines the level of stress concentration and, hence, the failure stress. Even micron-sized surface flaws cause stress concentrations which significantly reduce the tensile strength of the fibers.
Long lengths of light guide fibers have considerable potential strength, but the strength is realized only if the fiber is protected with a layer of a coating material such as, for example, a polymer, soon after it has been drawn from a perform. This coating serves to prevent airborne particles from impinging upon and adhering to the surface of the drawn fiber and to prevent the surface of the fiber from coming into contact with atmosphere moisture, which would weaken it and possibly affect its transmission properties. Also, the coating shields the fibers from surface abrasion, which could occur as a result of subsequent manufacturing processes and handling during installation. The coating also provides protection from corrosive environments and spaces the fibers in cable structures.
Light guide fibers are usually coated during a coating process which typically involves drawing the light guide fiber through a reservoir of a liquid prepolymer material and then curing the liquid prepolymer material to harden it by exposing it to curing radiation, which normally is ultraviolet light. Ultraviolet light (UV) curing lamp systems are used to cure optical fiber coatings. Such lamp systems typically contain an array of focusing mirrors that focus the light from an ultraviolet bulb onto the product to be cured. Since the ultraviolet bulbs of the curing lamp systems generate a substantial amount of heat, the housing of the lamp system must be cooled to prevent damage to the internal components of the lamp system.
During the curing process, the fiber passes through a quartz center tube that runs the length of the focusing mirror assembly. The coating on the fiber will not cure properly in the presence of oxygen. Therefore, nitrogen gas (N2) is pumped through the center tube in order to purge the oxygen from the center tube. If an air seal on the center tube becomes defective, or if a fracture in the center tube exists, air will enter the center tube, which will prevent the coating from being properly cured.
Also, if the UV bulb does not generate a sufficient amount of UV) radiation, the coating will not be properly cured. Also, dust and other particulates may accumulate on the parabolic mirrors and/or on the glass surface of the center tube, which may prevent sufficient UV radiation from reaching the coating on the optical fiber. These factors may also prevent the coating from being properly cured.
Therefore, the conditions of various components within the UV curing lamp system affect the curing process. When the LW curing lamp system is not functioning properly due to one of the aforementioned factors, the coating on the optical fiber will not be properly cured, which will result in defective optical fiber cables. It would be desirable to be able to detect when one or more conditions within the UV curing lamp system will result in the coating on the optical fiber not being properly cured so that the fiber manufacturing process can be halted until the faulty condition has been rectified. Currently, no techniques are utilized in the optical fiber manufacturing process to determine whether or not the conditions within the UV curing lamp system are suitable for properly curing the coating on the optical fiber.
UV curing lamp systems are used to cure other types of materials as well. For example, UV curing lamp systems are used to cure UV-curable inks, optical fiber over-coatings, etc. They are also utilized in the electronics industry. Currently, no techniques are used to determine whether or not these UV curing lamp systems are operating properly, or whether the inks are being properly cured.
Accordingly, a need exists for a method and apparatus for determining whether or not the conditions within a UV curing lamp system utilized in a UV curing process are adequate to properly cure whatever UV curable material is being cured in the UV curing lamp system.
The present invention provides a method and apparatus for monitoring a UV curing lamp system to determine whether or not the UV curing lamp system is operating properly and/or whether or not the UV-curable material is being properly cured. The UV curable material may be, for example, a UV-curable optical fiber coating layer or a UV-curable ink. A sensor is disposed to measure the temperature of gas being exhausted from a center tube of the UV curing lamp system. The center tube typically has nitrogen gas pumped into it to purge air from the center tube. The optical fiber having the UV-curable material (e.g., a coating layer) thereon passes through the center tube. If a defect exists in the center tube, or if insufficient UV radiation is reaching the UV-curable material, the temperature of the gas stream exhausted from the center tube will drop. The temperature of the gas is measured and compared to first and/or second threshold values to determine whether a defect in the center tube exists and/or whether insufficient radiation is reaching the UV-curable material, respectively.
These determinations preferably are made by a computer, but also may be made by a simple comparator circuit or by a human being. In accordance with the preferred embodiment, the determinations are made by a computer. The computer performs a defect detection method that compares the temperature with the first and/or second threshold values. The computer may be the computer that controls the operations of the optical fiber manufacturing process and may halt the manufacturing process upon determining that the UV-curable material is not being properly cured. The computer may also be a separate computer.
Other features and advantages of the present invention will become apparent to those skilled in the art from the following description, drawings and claims.